Hydraulic torque converters, devices used to change the ratio of torque to speed between the input and output shafts of the converter, revolutionized the automotive and marine propulsion industries by providing hydraulic means to transfer energy from an engine to a drive mechanism, e.g., drive shaft or automatic transmission, while smoothing out engine power pulses. A torque converter includes three primary components: an impeller, sometimes referred to as a pump, directly connected to the engine's crankshaft; a turbine, similar in structure to the impeller, however the turbine is connected to the input shaft of the transmission; and, a stator, located between the impeller and turbine, which redirects the flow of hydraulic fluid exiting from the turbine prior to reentry into the pump, thereby providing additional rotational force to the pump. This additional rotational force results in torque multiplication. Thus, for example, when the impeller speed is high and the turbine speed is low, torque may be multiplied by a 2:1 or higher ratio, whereas when the impeller and turbine speeds are approximately the same, torque can be transferred at about a 1:1 ratio.
A separate shaft emanating from the transmission, i.e., the stator shaft, enters the torque converter and provides a rotationally fixed mount for the stator. Often torque converters include a one-way clutch between the stator and the stationary stator shaft which permits the stator to rotate in response to changing fluid forces resulting from increased turbine speed, i.e., as the turbine speed increases in response to increased pump speed. Thus, when the pump rotates more quickly than the turbine, the stator remains stationary. While contrarily, as the turbine rotation speed approaches the speed of the pump, the stator begins to rotate due to increased fluid forces. When the turbine rotates at substantially the same speed as the pump, the stator freewheels, and as described supra, torque is transmitted at approximately a 1:1 ratio between the engine and the transmission.
A prior art stator having a one way clutch is shown in FIGS. 1A and 1B. The above-described stator 10 broadly comprises stator casting 12, outer race 14 and inner race 16. Stator casting 12 is rotationally fixed to outer race 14, and under various conditions, outer and inner races 14 and 16, respectively, are either rotationally fixed or free to rotate relative to each other. Springs 18 and rollers 20 are disposed about and between outer and inner races 14 and 16, respectively. During instances when the pump rotates more quickly than the turbine, i.e., the stator remains stationary, springs 18 have sufficient force to press rollers 20 within wedged areas 22, i.e., the area formed between outer and inner races 14 and 16, respectively. (See FIG. 1B). During such conditions, the inner and outer races are rotationally fixed to each other thereby preventing stator casting 12 having blades 24 from rotating. Thus, in this instance, stator 10 redirects the fluid passing from the turbine back to the pump. During instances when the pump rotates at substantially the same speed as the turbine, i.e., the stator freewheels. During such conditions, the blades rotate in the direction of the pump and fluid is not redirected as it passes from the turbine to the pump. In short, during a lockup condition, stator 10 is rotationally fixed to the transmission housing via the stator shaft, while during a freewheel condition, stator 10 may freely rotate relative to the stator shaft and thereby the transmission housing.
In addition to the above described one way clutch for a torque converter stator, many other arrangements have been disclosed in the art. For example, several manufacturers have designed ratchet type one way clutches which use individual strut elements in both radial and axial directions. See, for example, U.S. Pat. No. 6,907,971 which discloses a ratchet type clutch system that is designed to enable lockup of the ratchet in one direction and slippage in the opposite direction.
The prior art one way clutch designs have a variety of problems. For example, the one way clutch type shown in FIGS. 1A and 1B, also known as roller and sprag clutches, are expensive due to high component costs combined with high assembly costs. Although the ratchet type one way clutches, for example having individual struts, have lower component costs, this type of one way clutch still is expensive to assemble.
As can be derived from the variety of devices and methods directed at providing a one way clutch in a torque converter stator, many means have been contemplated to accomplish the desired end, i.e., clutch lockup below a particular torque level and clutch freewheeling above that particular torque level. Heretofore, tradeoffs between component and assembly cost and performance were required. Thus, there is a long-felt need for a one way clutch for a torque converter stator that is easy to assemble, includes inexpensive component parts and provides a high level of performance.